Chances of life appearing

[JohnClay]

Sorry if my maths or science is wrong…
note: I don’t believe in intelligent design. The reason why I think life seems incredibly unlikely and yet it happened is because I think there are a near-infinite number of parallel histories of the universe and therefore whatever could happen did in some of the parallel histories. So some universes could even have life independently appearing billions of times.

Firstly, some stuff about the origin of life:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AbioticSynthesis.html

I was wondering what people think would be the number of units big a sequence of bases would be in order for it to be considered “life” or at least be self-replicating…

I have assumed it would be a million units long.

To make it as likely as possible let’s assume there are only 2 bases. The odds of a random sequence of a million bases being in the right sequence would be 1 in 2^million (2 to the power of a million). 2^10 = 1000 = 10^3, so 2^million = 10^300,000.
Say there are 10^100,000 (1 with 100,000 zeroes) different combinations that also result in a self-replicating molecule.
That means the odds of a random sequence of a million bases resulting in life is 1 in 10^200,000.

Let’s assume that every bit of space in the observable universe is only made up of those 2 bases:

Observable universe | Size

= 10^80 cubic metres.

1 cubic metre = 1,000 litres = 1,000 kg = 1,000,000 grams of water.

Say the bases are about as dense as water.

http://library.thinkquest.org/19957/atomic/molebody.html
http://tannerm.com/avogadro.htm
(a mole) 6.02 x 10^23 water molecules would weigh 18.0153g.

1,000,000g / 18.0153g = 55,508 moles = (* 6.02 x 10^23)
= 33,415,816,000,000,000,000,000,000,000
= 3.3 x 10^28
= 10^30 (being generous) base molecules per cubic metre
= 10^110 base molecules if they filled the observeable universe

or let’s try to put even more molecules into a cubic metre…

Planck units

smallest unit of length = 10^-35 metres
so a cubic metre would contain 10^105 cubic planck lengths.
= 10^185 base molecules if they filled the observeable universe
in that case the molecules would be smaller than subatomic particles though…

say the molecules are each conveniently divided into groups of a million…
= 10^179 sets of a million molecules.

Planck units

smallest unit of time = 10^-44 seconds

number of seconds in history of universe
= 14,000,000,000 yrs x 365 x 24 x 60 x 60
= 441,504,000,000,000,000
= 10^18 seconds
= 10^18 * 10^44 = 10^62 units of time in history of universe

say every planck time, the 10^179 sets of molecules randomly change…

in the history of the universe there would be
10^(62+179) = 10^241 combinations of molecules.

It would take almost 10^200,000 histories of the universe to create a self-replicating molecule… and there would have to be a mechanism to stop it from being automatically changed into another combination of molecules.

Rubik's Cube | Permutations

BTW, apparently there are about 10^19 combinations in the rubik’s cube… with one 1 right combination.

[Der_Trihs]

One problem with such calculations is that the combinations AREN’T random. Life is formed of molecules with a tendency towards self-organization. Another problem is that a replicator doesn’t need to be a million bases long; replicating molecules can be less than a hundred bases long.

I do give you points for the parallel world idea being more sensible than claiming “Goddidit”.

[Jonathan_Chance]

The problem with such calculation isn’t that you can’t defend them. Clearly you can.

However we have a sample size of one (Earth) and life occurred here. So in places with conditions in which life could appear it has appeared 100% of the time. We need more empirical data before any real judgment can be made. Maybe there’s something evolved on Europa. The only real way to add to the data is to get out there somehow and see if there’s anything there.

So for all the unlikelihood of life occurring it clearly has. Not only that but in the one sample we have it not only occurred but developed sentience and so forth.

[JohnClay]

@Jonathan_Chance

…However we have a sample size of one (Earth) and life occurred here. So in places with conditions in which life could appear it has appeared 100% of the time…So for all the unlikelihood of life occurring it clearly has. Not only that but in the one sample we have it not only occurred but developed sentience and so forth.

Many-worlds interpretation

Assuming that the Many-worlds interpretation of quantum mechanics is true, there are many versions of Earth - not just one. And only those versions which evolved sentient life would be debating this. Those without life would just be silent.

[JohnClay]

@Der_Trihs

One problem with such calculations is that the combinations AREN’T random. Life is formed of molecules with a tendency towards self-organization.

BTW have scientists solved the following problem yet:

Handedness Could Reveal Aliens

“When chemists synthesize organic compounds in the lab, they often wind up with a mix of molecules: half are right-handed, and half are left. But cells are a bit more particular. When life arose, our ancestors made some choices. They went with the right-handed sugars, and the left-handed amino acids, a tradition still in effect.”

Another problem is that a replicator doesn’t need to be a million bases long; replicating molecules can be less than a hundred bases long.

Hmmm… I didn’t realize self-replicating molecules had been made already…
e.g.

Self-Replicating Chemicals Evolve Into Lifelike Ecosystem

[Strinka]

You also assume that there is only one “correct” sequence for the first self-replicating molecule, which can’t be correct. As evidence, human DNA self-replicates, and bacteria DNA self-replicates, but they’re not the same. There’s no reason to think that simpler self-replicators would have to have one specific form.

[Simplicio]

Your assuming their’s one unique base sequence that count’s as “life”, that’s empirically not true, since presently on Earth living things have billions of differing sequences of bases.

[JohnClay]

Strinka & Simplicio:
“living things have billions of differing sequences of bases”

i.e. 10^9

Well I wrote:

Say there are 10^100,000 (1 with 100,000 zeroes) different combinations that also result in a self-replicating molecule.

[Simplicio]

Ah, sorry, missed that.

Still, I think the percentage of base pair combinations that lead to self replication is probably considerably higher, and the minimal size for the number of base pairs is much lower (I believe some modern viruses are on order of 100k pairs). We don’t need something that we’d recognize as living today, just something that can do the bare minimum of self-replication for evolution to get a grip.

Interesting OP though.

[Half_Man_Half_Wit]

That’s a lot of numbers clashed together without much sense, essentially Hoyle’s fallacy all over again. The problem is that nobody claims life arose by a purely random coalescence of molecules. Instead, it developed, through a series of progressively more complex intermediaries – starting out with simple chemical reactions, giving us monomers (single amino acids), which are precursors to nucleotides, the components of both RNA and DNA, which themselves tend to form short-lived bonds between each other, which are generally broken apart rather quick, but sometimes show self-catalyzing properties, effectively lowering the energy needed for their own creation, which in turn increases the rates at which such chains are build up, which makes it possible to create longer chains faster than they are broken down, basically leaving you with strands of RNA able to catalyze their own reproduction; from there on, natural selection takes over (at least, it happened that way in one current model, the so-called RNA world hypothesis). I’m no expert in the field, so I may have confused the argumentation at some point, but the main principle – that life arose through self-organizing processes rather than random coalescence – is valid regardless. There’s some good videos illustrating some current hypotheses on YouTube – here are two.

[Strinka]

So you did. I stand corrected.

I will note that this

2^10 = 1000 = 10^3, so 2^million = 10^300,000.

is not correct.

If it were, 2^100 would equal 10^30, but according to google, 2^100 = 1.2676506×10^30. Not such a huge difference (only 2.676506×10^29), but it would get much larger as you keep tacking on zeros.

Of course, that makes your numbers larger, so you only underestimated…

[JohnClay]

say the sequence is 100 units long…

with 2 bases: (not realistic)
2^100 = 10^30

with 20 bases: (e.g. using only amino acids, with the right handedness)
20^100 = 10^130

The number of sets of molecules is very exaggerated though…

Observable universe

“Estimates of the matter content of the observable universe indicate that it contains on the order of 10^80 atoms”

Say there are 10^80 sets of 100 molecules each…
in the history of the universe there would be
10^(62+80) = 10^142 combinations of molecules.

[JohnClay]

@Strinka

If it were, 2^100 would equal 10^30, but according to google, 2^100 = 1.2676506×10^30. Not such a huge difference (only 2.676506×10^29), but it would get much larger as you keep tacking on zeros…

Well 2^10 = 1024 which is about 10^3 (1000). This problem is also found when you compare 1 gigabyte with how many bytes it actually is (1073741824), etc.

[JohnClay]

Half Man Half Wit:
Thanks for your comments… btw are there still very simple self-replicating molecules (RNA?) in nature? These fairly recent advances in knowledge are pretty convincing. (btw I used to be a young earth creationist)

[Half_Man_Half_Wit]

@JohnClay

Half Man Half Wit:
Thanks for your comments… btw are there still very simple self-replicating molecules (RNA?) in nature?

Not that I know of – the atmosphere these days contains way too much oxygen, which is too aggressively reactive to allow the outlined generative processes to happen. They have, however, been created in the lab, and so have all the component parts.

[Smeghead]

I strongly strongly recommend the book “At Home in the Universe” by Stuart Kaufmann, which examines this question in detail. He presents some very compelling arguments, backed up by some very clever computer modeling, that life is not only wildly unlikely, but possibly all but inevitable given a complex enough system.

[JohnClay]

Smeghead:
Sorry I think I’ll only get around to watching youtube videos or reading some articles on the internet.

[ITR_champion]

@Half_Man_Half_Wit

That’s a lot of numbers clashed together without much sense, essentially Hoyle’s fallacy all over again. The problem is that nobody claims life arose by a purely random coalescence of molecules. Instead, it developed, through a series of progressively more complex intermediaries – starting out with simple chemical reactions, giving us monomers (single amino acids), which are precursors to nucleotides, the components of both RNA and DNA, which themselves tend to form short-lived bonds between each other, which are generally broken apart rather quick, but sometimes show self-catalyzing properties, effectively lowering the energy needed for their own creation, which in turn increases the rates at which such chains are build up, which makes it possible to create longer chains faster than they are broken down, basically leaving you with strands of RNA able to catalyze their own reproduction; from there on, natural selection takes over (at least, it happened that way in one current model, the so-called RNA world hypothesis). I’m no expert in the field, so I may have confused the argumentation at some point, but the main principle – that life arose through self-organizing processes rather than random coalescence – is valid regardless. There’s some good videos illustrating some current hypotheses on YouTube – here are two.

As I understand it, there are several problems with the theory you propose.

First of all, there’s no reason to believe that early earth contained a ready supply of amino acids, much less that it contained the right amino acids, in the right proportions, with the right orientation. (Or rather the left orientation, as John Clay mentioned already.) Like most people I was taught about the Miller-Urey experiment in school, and was told that this produced all 20 amino acids necessary for life. But my science teacher did not mention that the conditions of the experiment were highly idealized, and not at all relevant to early earth. The experiment used a mixture of methane and ammonia, but the early earth atmosphere was actually a mixture of carbon dioxide and nitrogen.

Second, there’s no reason to believe that early earth had ribose sugars present in significant quantities, and those sugars are necessary for any molecule RNA or DNA. While there are potential pathways by which those sugars could have formed, the sugars would have lasted only a short time.

The existence of the RNA world, in which RNA acted as a catalyst as well as an informational macromolecule, assumes a large prebiotic source of ribose or the existence of pre-RNA molecules with backbones different from ribose-phosphate. The generally accepted prebiotic synthesis of ribose, the formose reaction, yields numerous sugars without any selectivity. Even if there were a selective synthesis of ribose, there is still the problem of stability. Sugars are known to be unstable in strong acid or base, but there are few data for neutral solutions. Therefore, we have measured the rate of decomposition of ribose between pH 4 and pH 8 from 40 degrees C to 120 degrees C. The ribose half-lives are very short (73 min at pH 7.0 and 100 degrees C and 44 years at pH 7.0 and 0 degrees C). The other aldopentoses and aldohexoses have half-lives within an order of magnitude of these values, as do 2-deoxyribose, ribose 5-phosphate, and ribose 2,4-bisphosphate. These results suggest that the backbone of the first genetic material could not have contained ribose or other sugars because of their instability.

Third, even if we had the amino acids and the ribose, there’s no reason to believe that we’d get the nucleotides. Research has shown that:

Many accounts of the origin of life assume that the spontaneous synthesis of a self-replicating nucleic acid could take place readily. Serious chemical obstacles exist, however, which make such an event extremely improbable. Prebiotic syntheses of adenine from HCN, of D,L-ribose from adenosine, and of adenosine from adenine and D-ribose have in fact been demonstrated. However these procedures use pure starting materials, afford poor yields, and are run under conditions which are not compatible with one another. Any nucleic acid components which were formed on the primitive earth would tend to hydrolyze by a number of pathways. Their polymerization would be inhibited by the presence of vast numbers of related substances which would react preferentially with them. It appears likely that nucleic acids were not formed by prebiotic routes, but are later products of evolution.

Fourth, even if we had the RNA nucleotides, there’s no reason to believe that they would link together into polymers. Contrary to what Der Trihs said above, it does not happen automatically, but rather

Joyce and Orgel discuss candidly the problems with this postulate. They note that nucleotides do not link unless there is some type of activation of the phosphate group. The only effective activating groups for the nucleotide phosphate group (imidazolides, etc.), however, are those that are totally implausible in any prebiotic scenario. In living organisms today, adenosine-5’-triphosphate (ATP) is used for activation of nucleoside phosphate groups, but ATP would not be available for prebiotic syntheses.

Fifth, even if polymerization was achieved, there’s no reason to believe that the self-catalyzing polymers would arise by chance. Which brings us right back to the sort of math that started the thread.

[Half_Man_Half_Wit]

@ITR_champion

As I understand it, there are several problems with the theory you propose.

As opposed to your theory, ‘a wizard did it’.

[Tom_Tildrum]

@JohnClay

Many-worlds interpretation - Wikipedia
Assuming that the Many-worlds interpretation of quantum mechanics is true, there are many versions of Earth - not just one. And only those versions which evolved sentient life would be debating this. Those without life would just be silent.

The MWI is an untestable philosophical proposition that just sounds science-y. There’s no real difference between saying “all these events are happening in an infinitude of unreachable other universes,” versus “all these events are happening in the mind of God.”